共查询到17条相似文献,搜索用时 31 毫秒
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新参考系的引入对天体测量学的影响 总被引:5,自引:0,他引:5
由于观测、参考架、模型、时间尺度精度的不断提高和完善,国际天球参考系(ICRS)被引入使用,IAU2000年大会决定从2003年起采用新的天球中介极(CIP)、新的天球中介原点(CIO)、新的岁差一章动模型和新的UTI定义等,并定义了新的中介的运动参考架,由此给天体测量学带来很大的影响,天体测量学的内容和实践发生了许多重要的变化。据此,对天体测量学的术语、概念和定义的变化作了描述,并讨论了变化的原因和对天体测量学的影响。新的一套天体测量理论和方法正在变更之中,我们应及时跟上这个领域的发展步伐。 相似文献
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本文根据基本天体测量的主要任务和目前发展趋势的要求,以及低纬子午环配备CCD后的观测精度、效率和极限星等,提出了该仪器长期观测;的目标,包括建立实用的准惯性天球参考架和动力学参考架,为太阳系动力学研究,为银河系结构和运动学研究,为某些天体物理课题研究的需要,提供有用的观测数据,为本地的地震预报和天文地震研究提供参考数据。在甚长基线射电干涉测量技术和空间测量技术迅速发展的时代,地面光学天体测量仍具有 相似文献
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本文根据基本天体测量的主要任务和目前发展趋势的要求 ,以及低纬子午环配备CCD后的观测精度、效率和极限星等 ,提出了该仪器长期观测的课题目标 ,包括建立实用的准惯性天球参考架和动力学参考架 ,为太阳系动力学研究 ,为银河系结构和运动学研究 ,为某些天体物理课题研究的需要 ,提供有用的观测数据 ,为本地的地震预报和天文地震研究提供参考数据。在甚长基线射电干涉测量技术和空间测量技术迅速发展的时代 ,地面光学天体测量仍具有其不可取代的优势 ,只要能高精度地测定仪器的各种误差 ,消除仪器重力变形和热变形的影响 ,并尽可能消除由地球大气因素引起的系统误差影响 ,取得与空间测量平均而言可比的观测精度 ,两者相互配合 ,取长补短 ,就能更好地为上述诸多课题目标开展观测和研究 ,促进天体测量学和有关学科的发展 ,文中对这些要求的实现作了必要的叙述。 相似文献
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本文评述了在建立历表参考架和恒星参考架过程中所面临的问题和困难,回顾了建立河外射电天球参考架的发展历史,并介绍了其目前状况,讨论了河外射电天球参考架在与其他天球参考架连接过程中所遇到的问题及其可能的解决途径。 相似文献
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本文评述了在建立历表参考架和恒星参考架过程中所面临的问题和困难,回顾了建立河外射电天球参考架的发展历史,并介绍了其目前状况,讨论了河外射电天球参考架在与其他天球参考架连接过程中所遇到的问题及其可能的解决途径。 相似文献
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O. A. Titov 《Astronomy Letters》2007,33(7):481-487
According to the most recent geodetic VLBI data, some of the radio sources that define the fundamental celestial reference frame are astrometrically unstable. In contrast to the stellar proper motions described by a linear function, the apparent proper motions of quasars are more complex. Therefore, they are difficult to approximate by a particular model. Being disregarded, the positional instability of the defining quasars can lead to a bias in the estimates of other parameters from observations, for example, the nutation angle corrections. 相似文献
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Linjie Chen Amin Aminaei Leonid I. Gurvits Marc Klein Wolt Hamid Reza Pourshaghaghi Yihua Yan Heino Falcke 《Experimental Astronomy》2018,45(2):231-253
In radio astronomy, the Ultra-Long Wavelengths (ULW) regime of longer than 10 m (frequencies below 30 MHz), remains the last virtually unexplored window of the celestial electromagnetic spectrum. The strength of the science case for extending radio astronomy into the ULW window is growing. However, the opaqueness of the Earth’s ionosphere makes ULW observations by ground-based facilities practically impossible. Furthermore, the ULW spectrum is full of anthropogenic radio frequency interference (RFI). The only radical solution for both problems is in placing an ULW astronomy facility in space. We present a concept of a key element of a space-borne ULW array facility, an antenna that addresses radio astronomical specifications. A tripole–type antenna and amplifier are analysed as a solution for ULW implementation. A receiver system with a low power dissipation is discussed as well. The active antenna is optimized to operate at the noise level defined by the celestial emission in the frequency band 1 ? 30 MHz. Field experiments with a prototype tripole antenna enabled estimates of the system noise temperature. They indicated that the proposed concept meets the requirements of a space-borne ULW array facility. 相似文献
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《天文和天体物理学研究(英文版)》2021,(4)
The very low frequency(VLF) regime below 30 MHz in the electromagnetic spectrum has presently been drawing global attention in radio astronomical research due to its potentially significant science outcomes exploring many unknown extragalactic sources,transients,and so on.However,the nontransparency of the Earth's ionosphere,ionospheric distortion and artificial radio frequency interference(RFI) have made it difficult to detect the VLF celestial radio emission with ground-based instruments.A straightforward solution to overcome these problems is a space-based VLF radio telescope,just like the VLF radio instruments onboard the Chang'E-4 spacecraft.But building such a space telescope would be inevitably costly and technically challenging.The alternative approach would be then a ground-based VLF radio telescope.Particularly,in the period of post 2020 when the solar and terrestrial ionospheric activities are expected to be in a 'calm' state,it will provide us a good chance to perform VLF ground-based radio observations.Anticipating such an opportunity,we built an agile VLF radio spectrum explorer co-located with the currently operational Mingantu Spectra Radio Heliograph(MUSER).The instrument includes four antennas operating in the VLF frequency range 1-70 MHz.Along with them,we employ an eight-channel analog and digital receivers to amplify,digitize and process the radio signals received by the antennas.We present in the paper this VLF radio spectrum explorer and the instrument will be useful for celestial studies of VLF radio emissions. 相似文献
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M. V. Sazhin V. E. Zharov A. V. Volynkin & T. A. Kalinina 《Monthly notices of the Royal Astronomical Society》1998,300(1):287-291
The fluctuation of the angular positions of reference extragalactic radio and optical sources under the influence of the irregular gravitational field of visible Galactic stars is considered. It is shown that these angular fluctuations range from a few up to hundreds of microarcseconds. This leads to a small rotation of the celestial reference frame. The non-diagonal coefficients of the rotation matrix are of the order of a microarcsecond. The temporal variation of these coefficients due to the proper motion of the foreground stars is of the order of one microsecond per 20 years. The celestial reference frame can therefore be considered inertial and homogeneous only to microarcsecond accuracy. Astrometric catalogues with microarcsecond accuracy will be unstable, and must be re-established every 20 years. 相似文献
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在简要阐明参考系、参考架及其历史重大进程的基础上,对几种重要的、最新规范的参考系/参考架(质心天球参考系和地心天球参考系、国际天球参考系、国际地球参考系、太阳系动力学参考系等)的定义、实现和特点作了评述和分析,并对最新规范中与参考系、参考架有关的某些新概念的定义和新模式的应用(自2003年开始贯彻),如:天球中介极(CIP)、天球历书原点(CEO)、地球历书原点(TEO)、地球自转角的新定义、岁差-章动新模式的应用,作了阐述和讨论。 相似文献
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George D. Nicolson 《Astrophysics and Space Science》1995,230(1-2):329-339
The Hartebeesthoek Radio Astronomy Observatory has played a key role in the development of very long baseline interferometry (VLBI) in the southern hemisphere since 1971. This paper describes how the VLBI programme evolved and the instrumentation used. Contributions to high resolution mapping of compact radio sources are described, for both the Southern Hemisphere VLBI Experiment, SHEVE, and for Global networks, where HartRAO has made significant improvements in the N-S resolution. The unique geographical location of the telescope has been used to establish the terrestrial reference frame in the southern hemisphere and to measure tectonic motions over the past nine years. The Observatory has also been a fundamental station in extending the celestial reference frame defined by extragalactic radio sources to the southern hemisphere, and results of these programmes are given. 相似文献
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H.O. Rucker M.Y. Boudjada M. Leitner A. Lecacheux M. Aubier A. Konovalenko P.H.M. Galopeau V. Shaposhnikov 《Astrophysics and Space Science》2001,277(1-2):325-328
Jupiter radio emission is known to be the most powerful nonthermal planetary radiation. In recent years specifically space-based
observations allow us to permanently cover a large frequency band(from 100 kHz up to 40 MHz combined with ground-based telescopes)of
the Jovian spectrum. The Plasma and Wave Science experiment onboard Galileo enables the observation of Jovian kilometric and
hectometric emissions; Wind/WAVES and ground-based telescopes (mainly Decametric Array in Nancay, France, and UTR-2 in Kharkov,
Ukraine) cover also hectometric and mainly decametric emissions. Specific geometrical configurations between Cassini approaching
Jupiter and Wind spacecraft orbiting Earth, with Galileo orbiting Jupiter and Wind, in combination with ground-based observations
provide a new approach to perform Jovian radio tomography. The tomography technique is used to analyze ray paths of Jovian
radio emission observed in different directions (e.g. solar and anti-solar direction) and for different declination of Earth.
The developments of Jovian radio emission tomography in recent years treated refraction effects and its connection to the
local magnetic field in the radio source as well as the radio wave propagation through the Io torus and the terrestrial ionosphere.
Most recently ground-based multi-site and simultaneous Jupiter decametric radio observations by means of digital spectropolarimeter
and waveform receiver provide the basis of a new data analysis treatment. The above addressed topics are without exemption
deeply connected to the plasma structures the radio waves are generated in and propagating through.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献